Method of rolling threads on thread forming tools



Jan. 11, 1955 1 w, BEDKER 2,699,077

METHOD OF ROLLING THREADS ON THREAD FORMING TOOLS Filed NOV. 20, 1950 FIGJ.

FIG.3.

FIGS. Fl 6.7.

INVENTOR.

LEO W. BED KER BYZ/ WwW

ATTORNEYS United States Patent METHOD OF ROLLING THREADS ON THREAD FORMING TOOLS Leo W. Bedker, East Detroit, Mich., assignor of one-half to Emma G. Bedker, East Detroit, Mich.

Application November 20, 1950, Serial No. 196,626

4 Claims. (Cl. 76-101) The present invention relates to thread forming tool and method and apparatus for making the same.

At the present time methods are known for rolling threads on parts in which the thread is held to a high degree of accuracy and has a very desirable finish imparted thereto by the rolling operation. Moreover, the rolling operation work hardens the thread thus producing a more efiicient article. However, the problem presented by rolling threads onto a tool which is itself later to be used in rolling threads on a work piece, is quite a different matter.

In threads rolled on a work piece the important consideration is the accuracy, finish and strength of the sides of the threads. The actual crest or tip of the thread need not be held to such accuracy nor are its physical properties of critical significance since ordinarily clearance exists between the tip of a thread and the root of the thread of the remaining part. On the contrary, the tip or crest thread formed on a tool which is subsequently to be used for rolling threads on a work piece is the part of the thread which is subjected to the greatest stress in thread rolling.

The present invention has as its primary object the provision of a thread rolling tool, the threads of which are produced by a rolling operation which produces superior physical properties. The thread rolling tool is produced by a special rolling tool and is produced by a particular method different from the method of rolling threads on a work piece.

It is an object of the present invention to provide a special tool for rolling threads onto a thread rolling tool characterized by the provision of relief at the roots thereof permitting the rolling of excess material to and beyond the theoretical crest of the thread on the thread rolling tool.

It is a further object of the present invention to provide a novel method of rolling threads onto a thread rolling tool in which excess material is rolled up into the threads and rolled outwardly of the threads beyond that portion thereof which is employed in rolling threads onto the work piece.

Other objects and features of the invention will be come apparent as the description proceeds, especially when taken in conjunction with the accompanying drawings, wherein: I

Figure l is a side elevation of a thread roll holder suitable for supporting the special thread rolls used in rolling threads onto a thread rolling tool.

Figure 2 is a perspective view of a thread rolling tool according to the present invention.

Figure 3 is a fragmentary perspective view of a flat thread rolling die according to the present invention.

Figure 4 is a transverse section through a thread of a thread rolling tool.

Figure 5 is a transverse sectional view through a partially rolled thread.

Figure 6 is a transverse sectional view through a rolled thread as produced by known methods of thread rollmg.

Figure 7 is a transverse sectional view showing the relationship between a completely rolled thread when rolled in accordance with the present invention, and the special thread rolling tool employed for rolling the thread.

Referring now to Figure 1 there is illustrated a holder 10 supporting a pair of thread rolls 12 and 14, these thread rolls being adjustable toward and away from each 2,699,077 Patented Jan. 11, 1955 "ice other by virtue of the elongated slot 16 and set screws 18 and 20 provided in association with the thread roll 12. A gear 22 is connected to the thread roll 14 and is connected to a second gear 24 secured to the thread roll 12 through a train of gears 26, 28, and 30. The relationship is such that rotation of either roll 12 or 14 upon contacting a rotating work piece will be transmitted to the other roll of the pair so as to insure proper alignment between the threads of the rolls as they come into simultaneous engagement with opposite sides of the rotating work piece. Threads rolled on a work piece such as indicated at W, are characterized by the fact that the material constituting each thread is rolled up out of the round stock substantially uniformly from both sides of the thread, thus producing a thread which is not only symmetrical in shape but also symmetrical as to distribution and character of metal therein. The thread rolling operation tends to dispose the structure of the metal parallel to the thread surface and in addition imparts a cold working thereto which hardens the thread.

In Figure 2 there is illustrated one of the thread rolls of a pair, as for example the roll 12, the other roll 14 being identical therewith.

Instead of rolling threads between pairs of opposed rolls as indicated in Figure 1, a similar result may be accomplished employing a pair of opposed flat thread die plates 30 as illustrated in Figure 3. In order to carry out the rolling operation a work piece is engaged at opposite sides by spaced parallel thread rolling dies which are then moved relative to each other to impart a rolling motion to the part being threaded.

At the present time thread rolls such as illustrated at 12 in Figure 2, or 30 in Figure 3, are produced by a grinding operation which is time consuming and expensive. Moreover, due to the inherent wear of any grinding wheel, it is impossible to produce thread rolls or thread die plates by grinding which are precisely accurate. According to the present invention thread forming tools, either rolls or die plates, are produced by a rolling operation. However, the problem of providing threads on a thread rolling tool is quite different from the problem of rolling threads on a work piece. In a work piece the tips of the threads ordinarily have clearance with the roots of the part to which they are threaded so that the accuracy and the physical properties of the metal at the crest of the thread is of no practical significance. On the contrary, in a thread rolling tool the precise shape and physical properties of the thread at its crest is of prime importance. It is this part of the thread which first engages a work piece and which is therefore subjected to the greatest amount of stress and wear.

Referring now to Figure 4 there is illustrated the crosssectional shape desired in a thread forming tool. The particular thread 40 illustrated is American standard 60 degree thread. It will be observed that each thread is provided at its top with a flat or land 42 and the root space between adjacent convolutions of the thread is also flat as indicated at 44.

Referring now to Figure 5 there is illustrated the crosssectional shape of a partially rolled thread 45. It will be observed that the metal of the thread is being rolled upwardly toward the crest from both sides, thus producing two separate rolls 46 of metal. The condition illustrated in Figure 5 is one which would exist if the thread rolls 12 and 14 of Figure 1 Were spaced apart further than the theoretically correct center distance.

Referring now to Figure 6 there is illustrated the condition of a completely rolled thread 50. In this figure it will be observed that the two independent rolls 46 have been forced together by the converging sides of the tool performing the rolling operation, thus producing a crevice 48 which extends down into the crest of the thread for an appreciable distance. The thread 50 would be perfectly satisfactory for use as a thread on a work piece but would be totally unsatisfactory for use as a thread on a thread forming tool. To bring the thread 50 of Figure 6 to the desired configuration illustrated at 40 in Figure 4, would require removal of metal at the crest of the thread along the line 52 which it will be observed is intersected by the crack or crevice 48. Thus if the thread 50 with the crest removed to provide a flat land such as shown at 42 in Figure 4, were employed on a thread rolling tool, the crest of the thread would be weakened by the portion of the crevice 48 remaining therein;

To overcome the foregoing difficulty a special tool is provided for rolling the threads on a thread rolling tool. The special tool may be in the form of a thread roll generally similar to the rolls 12 and 14 shown in Figures 1 and 2, or the die 30 shown in Figure 3. However, an important modification is required to render such thread rolling tools suitable for rolling threads on a thread rolling tool. The modification is best illustrated in Figure 7 in which a portion of a thread rolling tool 60 is illustrated shown in forming relation to a thread forming tool 62 on which the threads 64 are being rolled. The special tool 60 is provided with a thread 66, adjacent convolutions of which are shown as engaging a single convolution of the thread 64. So far as the present invention is concerned the special tool 60 may be either a roll or a thread forming die plate. In the space between the threads or the adjacent convolutions of a single thread if employed, clearance is provided as illustrated by the slot 68. The slot 68 is of less width than the desired width 42 to be finally produced on the top of the thread of the thread rolling tool. It is of sufficient depth to permit metal from the thread 64 to be rolled up into the groove as illustrated at 70 in Figure 7. Inasmuch as excess metal was rolled up into the groove 68, the slot or crevice 72 inherently produced between the rolls of metal at apposite sides of the thread is thus displaced upwardly. It is essential that the upward displacement of the metal at the crest of the thread shall be sufficient so that when the rolled thread 64 is finished by grinding off the crests of the threads down to a line indicated at 74 so as to produce a land such as shown at 42, the land surface will not be intersected by the crack or crevice 72.

It is found that thread forming tools either in the form of rolls or fiat thread forming dies, on which the threads have been produced by rolling, are superior in several respects to the ground threads which have previously been employed. In the first place the threads are characterized by an improvement in the grain structure of the metal due to the rolling operation. In the second place, the surface is better than a ground surface, the thread rolling operation producing a mirror smooth surface thereon. Finally, it is found that greater accuracy may be maintained by rolling the threads on the thread rolling tool than has heretofore been possible in commercial production with thread grinders.

While the tool has improved characteristics over previously known ground tools, perhaps the most important advantage is in the reduction of cost. Thread forming tools may be produced by rolling threads thereon in an insignificant fraction of the time required to produce the threads by grinding. The final operation of grinding off the crests of the threads as suggested in the description of Figure 7 to produce the lands shown in Figure 4, is a simple operation since it is essentially a cylindrical grinding operation.

It is desired to emphasize the fact that the present method and the use of the present special tool for rolling threads on thread rolling tools, is not applicable to the rolling of a threaded work piece since it results in the production of excess material at the crest of the threads which would interfere with the operation of the thread as an ordinary thread mating with a similar threaded part.

While particular emphasis has been laid in the foregoing on the rolling of threads on a thread roll, it will be readily apparent that the invention may be practiced equally well in rolling threads onto a fiat thread forming die plate. In this case the special tool employed is in the form of a round member having a thread formed thereon. When this round member is caused to roll between the fiat plates, the threads on the round special tool roll the metal of the plates up into threads. The special tool employed again requires the presence of the relief groove or slot between the roots of the threads to provide for flow of excess metal subsequently to be removed.

From the foregoing it will be apparent that the present invention contemplates the production of thread rolls employing special tools in the form of specifically modified thread rolls; the production of thread rolls employing special tools in the form of specifically modified flat thread die plates; and the production of flat thread forming die plates employing a specifically modified thread roll as the forming tool. In all cases the special tool for rolling threads on the thread rolling tool is characterized by the provision of the relief groove or slot at the root between adjacent convolutions of the thread and the operation is characterized by the rolling of excess material up into the groove or slot to an extent sufiicient to permit final grinding of the thread to remove the crack or crevice inherently produced by the rolling operation along the crest of the thread.

The drawings and the foregoing specification constitute a description of the improved thread forming tool and method and apparatus for making the same, in such full, clear, concise and exact terms as to enable any person skilled in the art to practice the invention, the scope of which is indicated by the appended claims.

What I claim as my invention is:

1. The method of rolling threads on a thread forming tool which comprises rolling the material of the tool into thread form with substantially equal quantities of metal displaced into the thread at apposite sides thereof thereby forming outwardly extending rolls of metal at the sides of the crest of the thread, rolling excess metal into the thread to displace the crest of the thread including its outwardly extending rolls of metal beyond the crest desired in the finished tool, and then removing the metal in the said rolls of metal at the crest of the rolled thread.

2. The method of rolling threads on a thread forming tool which comprises rolling the material of the tool into thread form with substantially equal quantities of metal displaced into the thread at opposite sides thereof thereby forming outwardly extending rolls of metal at the sides of the crest of the thread, rolling excess metal into the thread to displace the crest of the thread including its outwardly extending rolls of metal beyond the lines of convergence of the sides of the thread, and then removing the metal in the said rolls of metal at the crest of the rolled thread.

3. The method of rolling a thread on a thread forming tool which comprises rolling the material of the tool into thread form by displacing substantial equal quantities of metal into the thread at opposite sides thereof and working the metal outwardly into thread form while confining the sides of the thread thus formed to a zone near the tip thereof corresponding to the final desired height of thread, during the aforementioned steps forming outwardly extending rolls of metal at the intersection between the sides and the top of the partially formed thread, with a crevice therebetwcen at the crest of the partially formed thread, thereafter rolling additional metal into the thread form while continuing to confine the sides of the thread outwardly to said zone and leaving the crest portion of the thread being formed outwardly beyond said zone free for outward displacement, continuing outward displacement of metal into the thread being formed to displace the crevice between said rolls at the crest of the thread outwardly beyond said zone, and finally removing the crest portion of the thread to remove the metal rolls and crevice therebetween.

4. The method as defined in claim 3 which comprises the step of rolling additional metal into the thread form to displace the crest of the rolled thread outwardly beyond the lines of convergence of the sides of the thread.

References Cited in the file of this patent UNITED STATES PATENTS 175,426 Clarke Mar. 28, 1876 1,579,308 Graham Apr. 6, 1926 1,773,471 Berg Aug. 19, 1930 1,830,926 Burnish Nov. 10, 1931 1,855,668 Frayer Apr. 26, 1932 2,576,709 Afiieck Nov. 27, 1951 FOREIGN PATENTS 384,949 Great Britain Dec. 15, 1932 564,269 Great Britain Sept. 20, 1944 

